Steam producing process and products

ABSTRACT

In a process utilizing steam, the method of producing at least a portion of said steam, including heating a water-containing, solid substance for generating steam and capturing the generated steam for said process. A suitable solid substance is Al(OH) 3 . New alumina products are obtained.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method of producing steamfor steam-consuming processes.

This, as well as other objects which will become apparent in thediscussion that follows, are achieved according to the presentinvention, by heating a water-containing, solid substance for generatingsteam.

The invention has particularly advantageous application in conjunctionwith water removal from aluminum hydrox:ide to prepare aluminaparticularly as feed for the Hall-Heroult electrolytic process forproducing aluminum metal. The aluminum hydroxide, in a moist or drycondition, is heated in a decomposer under self-fluidizing conditions,or fluidized by steam, and without contact by exhaust gases from fuelcombustion, so that pure steam is obtained. Pressures are typically inthe 20 to 500 psia range, in order that the steam will be at pressuresuitable for use. This steam is available for use as process steam in aBayer refining plant and also for power generation in usual steamengines or turbines. New alumina products are obtained. An importantadvantage achieved is that there is less breakage of particles duringwater removal than is the case during the flash or kiln calcination,prior art techniques of water removal. An additional advantage is thatan alumina product can be obtained which is characterized by a reducedamount of the parallel fissuring typifying alumina from atmosphericpressure, flash and kiln calcination of aluminum hydroxide. The aluminaproduct of this invention is stronger than alumina produced inatmospheric-pressure calcination processes, as indicated by lowerattrition indices. As an added benefit, differential calorimetry testsshow the process using about 10% less energy as compared to flash orkiln calciners, this saving being in addition to the energy savingsachieved by utilizing the steam coming from the aluminum hydroxide.

The production of essentially pure steam from aluminum hydroxide(alumina trihydrate, or "hydrate" for short) can be carried out using avariety of energy sources. Both direct and indirect heating methods arepossible. The heating method most applicable for retrofit to an existingcalciner is the use of hot combustion gasses from the furnace section ofthe calciner to indirectly heat the hydrate. Other heating methods forindirect heat transfer include electrical resistance heating, hot oil orsalt baths, heating by inductance, lasers, plasmas, combustion of coal,microwave radiation, nuclear and chemical reactors. The heat source mayoriginate from another process, such as the use of hot gasses from acoal gasification unit to decompose hydrate, or the hydrate may beindirectly decomposed while acting as a coolant to control a highlyexothermic reactor.

Direct heat transfer methods for drying and decomposition of hydrate toform an alumina product and pure steam include the use of in-bed,electrical resistance heating, microwave generators, lasers and/orsuperheated steam.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C compose a process flow schematic of an embodiment of theinvention.

FIG. 2 is a schematic of an alternative apparatus for use in the processof FIG. 1.

FIGS. 3 and 4 are scanning electron micrographs, at 12,000 timesmagnification; FIG. 3 being of a product of the invention and FIG. 4being of a product of the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A. Continuous Process

The invention finds a preferred setting in conjunction with the Bayerprocess for producing alumina from bauxite. The Bayer process utilizessteam, for instance, in its digester, where bauxite ore previouslycrushed in a grinder is treated with sodium hydroxide solution todissolve aluminum values. Steam provides the heat needed to maintain thetemperature and pressure conditions of the slurry in the digester. Theseare typically in the 100° to 300° C. and 100 to 500 pounds per squareinch absolute pressure (psia) ranges.

Steam is also used, e.g., in the evaporator of a Bayer plant.

Taking the digester as an example, the steam may heat the slurrydirectly by being injected right into the slurry--for instance, througha pipe opening below the slurry surface. Alternatively, the steam mayheat the slurry indirectly by supplying heat to a heat exchanger incontact with the slurry.

In general, it is of advantage that the steam be completely H₂ O, thuscontaining no diluting gases such as air. For instance, the steam shouldbe at least 50 volume-% water, preferably at least 75 volume-% water,and more preferably at least 94, or even 100, volume-% water. Oneparticular advantage of steam which is pure H₂ O is its characteristicof condensing at a constant temperature, such constant temperature beinga function of pressure. This is of use for temperature control in theprocess consuming the steam. For instance, 110 psia pure-H₂ O steamcondenses at about 175° C. and can be used to maintain a digestertemperature of about 150° C., the 25° C. difference being provided forheat transfer driving force.

If the steam is diluted with other gases, such as air, which isuncondensable at temperatures of interest for steam-consuming processes,the H₂ O in the steam condenses over a range of temperatures (as will beevident from the known variation of dew point with water vapor partialpressure). Additionally, the uncondensable gases represent a dilution ofthe great heat release obtained as H₂ O condenses, the heat released bythe uncondensable gases as they drop in temperature being relativelyinsignificant.

A diluting gas such as CO₂, for instance resulting from combustion of afuel containing carbon, is extremely disadvantageous in the case ofdirect steam heating in a Bayer process digester, because the CO₂ reactswith the NaOH needed to dissolve the aluminum values in the bauxite. TheNaOH loss occurs by reaction of the type

    2NaOH+CO.sub.2 →Na.sub.2 CO.sub.3 +H.sub.2 O

In the present invention it is proposed to carry out at least theinitial part of the calcination of aluminum hydroxide, "hydrate", byindirectly or directly heating the hydrate in a suitable, pressurizedcontainer vessel. This enables collection of steam released underpressure by the evaporation of the free moisture and removal of thechemically bound water. The separated steam can then be used in otherareas of the alumina refining plant, resulting in considerable energysavings. The partly calcined alumina product obtained from the pressuredecomposition vessel may then be calcined in conventional calcinationequipment such as a rotary kiln or a stationary calciner.

Thus, according to one embodiment of the present invention, steam forthe Bayer process is obtained by heating aluminum hydroxide, Al(OH)₃, toat least partially calcine it, with the evolved steam being captured fortransmission, e.g., to the digester. This is unlike previous methods ofcalcining Al(OH)₃, where, rather than being steam, the gases coming fromthe calcining are fuel exhaust containing water from the burning of thefuel and from the Al(OH)₃, an example of an analysis being, in volume-%,8% CO₂, 55.3% N₂, 2.5% O₂, and 34.2% H₂ O, as taken from the table onpage 34 of Schuhmann's Metallurgical Engineering, Volume 1, EngineeringPrinciples, Addision Wesley Press Inc., Cambridge, Mass. (1952). In suchprocesses, the burning, or burned, fuel-air mixture directly contactsthe Al(OH)₃ as it is being dehydrated.

A particular advantage of Al(OH)₃ as a solid used as a source of steamis that the steam is essentially 100%, i.e. pure, H₂ O. This is to becontrasted with, e.g., saw dust, where the steam might be contaminatedwith organic compounds also volatilizing during the liberation of thesteam.

It is estimated that about one-third of the steam requirement for aBayer process can be supplied from the water in the Al(OH)₃ product.

A principal equipment of the process is a decomposer vessel. Though thedecomposition process may be carried out by any combination of apressure vessel and indirect heating, an efficient method for carryingout this process is by the use of a fluidized bed. Our investigationshave shown that a bed of the hydrate exhibits self-fluidizing behavioron heating due to steam release on decomposition. High rates of heattransfer to the decomposing hydrate can thus be attained by utilizingthis self-fluidizing characteristic.

With reference now to FIG. 1, it illustrates an embodiment where theprocess of the invention is used in conjunction with a Bayer process.The segments of FIG. 1 show as follows:

FIG. 1A--A Bayer process utilizing steam from the process of theinvention;

FIG. 1B--Generating steam according to the invention;

FIG. 1C--A flash calciner for bringing partially calcined alumina fromFIG. 1B to a final, desired water-content suitable for use asmetallurgical alumina.

First with respect to FIG. 1A, bauxite from bauxite stockpile 10 isground in grinder 12 and then sent to digester 14, where it contributesto the solids portion of the slurry in the digester. The liquid portionof the slurry is a suitably concentrated, for example by evaporator 16,NaOH-containing, aqueous solution.

Following digestion, the slurry is fed to residue separation equipment18, which removes solids remaining from the digestion. Then, solution,free of solids, is fed to precipitator 20, where aluminum hydroxide,Al(OH)₃, crystalline form gibbsite, is precipitated. The resultingslurry is run through filter 22, to yield a solids portion through line24 and a liquids portion through line 26 going to evaporator forconcentration for recycle back to digester 14. The Al(OH)₃ filter cakesolids in line 24 will have both free moisture, to the extent of 8-16weight-%, and chemically bound water at 34.5 weight-% on dry Al(OH)₃.

Other steps may, of course, be in the Bayer process, for instance acausticization using lime. Thus, FIG. 1A is for the purpose ofillustrating how the steam generating process of the invention may becombined with a Bayer process in general, as an example of a steamconsuming process, rather than to go into the many fine points of aBayer process.

According to the invention, steam is generated for supply to thedigester and evaporator portions of the Bayer process through lines 28and 30 by heating Al(OH)₃ in decomposer 32 (FIG. 1B) to drive off freemoisture and chemically combined water from the Al(OH)₃. The equilibriumstate of the removed water is the gaseous state. The decomposer isoperated under pressure of suitable magnitude above one atmosphere (14.7psi) gage pressure to give the temperature desired during condensationof the steam in the Bayer process. The pressure may, for instance, be inthe range 20 to 250 psig (pounds per square inch gage pressure).

Feeder 34 is provided to transfer the Al(OH)₃ from essentiallyatmospheric pressure in line 24 to the elevated, e.g. 20 to 250 psig,pressure of the decomposer 32. Feeding equipment of the type describedin pages 99 to 120 of the publication "Workshop on Critical CoalConversion Equipment" for continuous feeding of coal from a low pressurestate to a high pressure state may be used for feeder 34. For example, asuitable feeder would be the Lockheed Kinetic Extruder shown in Slide6.22 on page 113 of that publication. Alternatively, the feeder could bea pair of lock hoppers, with one feeding under elevated pressure whilethe other is filling under atmospheric pressure, and vice versa, asillustrated by the Ducon Coal Feed System in Slide 6.26 on page 115.Further identifying information on this publication is as follows:Huntington, W.V. - Oct. 1-3, 1980, Harry W. Parker, Editor, TheEngineering Societies Commission on Energy, Inc., 444 North CapitolStreet, N.W., Suite 405, Washington, D.C. 20001, Date Published -January, 1981, Prepared for the United States Department of Energy,Under Contract No. EF-77-C-01-2468; FE-2468-88, Dist. Category LIC-90D.

These feeders permit decomposer 32 to be a continuously, orsemicontinuously in the case of e.g. lock hopper-type systems, operatingpressure vessel, where Al(OH)₃ entering chamber 36 falls into a numberof tubes 38, of which only three have been shown for schematic purposes.Tubes 38 are at a high temperature, for instance 250° to 650° C., sothat free moisture and chemically combined water are driven off assteam. This evolution of water in the gaseous state fluidizes theAl(OH)₃ particles in tubes 38. Residence time in the tubes is e.g. 10 to120 minutes.

The high temperature in the tubes is achieved by hot gases enteringchamber 39 through line 40 and leaving through line 42. Chamber 39 isenclosed by side walls 39a, top wall 39b and bottom wall 39c.

As the particles of Al(OH)₃ fall into tubes 38, they pile on top of oneanother to form a bed. The water evolved from them in the gaseous stateflows upwardly toward the vent to line 44 and is sufficient to fluidizethe particle beds in the tubes. This is termed self-fluidizing, in thatthe fluidizing gas comes from the particles themselves. During start-up,steam from an auxiliary steam source may be injected into chamber 52through line 53 to fluidize particles in the tubes 38, untilself-fluidization is achieved, after which line 53 may be closed. To theextent that the evolved water may not be enough to achieve desiredfluidization, such may be supplemented by steam injection through line53 during water removal from the Al(OH)₃. Steam feedback from line 44 toline 53 is another possibility. Feedback can be used, for example, tomaintain fluidization, or prevent bed particles from interbonding, whenthe process might be placed in idle, as when the need for steam in theBayer plant is temporarily diminished.

The steam product of the invention moves through line 44 to a solidsseparator such as cyclone 46, with solids being returned to thedecomposer through line 48 and steam going to the Bayer process throughline 50 to lines 28 and 30. It is estimated that steam from thedecomposer will make up one-third of the total steam needed by a Bayerprocess. The remaining two-thirds will enter line 50 through line 49 andwill come from one or more water boilers (not shown). In general, thesteam coming from the decomposer will be in a superheated condition, andthis may be cared for by heat loss in the lines or by a heat recoverydesuperheater (not shown) to bring the steam to its saturationtemperature at its location of use. For example, condensate returning towater boilers feeding line 49 may be preheated by running through such adesuperheater. Such condensate may also be used to get more heat fromthe gases in line 42.

The aluminum-bearing product resulting from removal of water from theAl(OH)₃ in tubes 38 collects in the chamber 52. It now comprisesparticles of boehmite and/or gamma alumina and X-ray indifferent (nowell-defined diffraction pattern) alumina pseudomorphous with aluminumhydroxide. Gamma alumina is somewhat on the borderline of being X-rayindifferent in that its diffraction pattern is not very well-defined.The product loss on ignition (LOI) (300° to 1200° C.) is in the rangefrom 1 to 12%, its surface area in the range 10 to 100 m² /g.

Interestingly, in the pressurized decomposer, there is less breakage ofparticles during water removal than is the case during the flash or kilncalciner, prior art techniques of water removal. In laboratory scaletests, there was no particle breakage as determined by "before" and"after" weights of the -325 mesh particle size fraction; in similarlaboratory scale tests for atmospheric pressure, flash or kiln calcinertests, it is typical to find that the -325 mesh size fraction increasesin weight by 2 to 5% due to particle breakage.

The aluminous product in chamber 52 is next conducted throughpressure-reducing feeder 54 (of the same construction as feeder 34) andline 56 to the flash calcining operation of FIG. 1C for further waterremoval to produce an alumina suitable for electrolysis in theHall-Heroult process for producing aluminum metal.

Alternatively, in the case where the higher temperature portion of the250° to 650° C. range in the decomposer has been used, the product inline 56 may be collected as feed for a Hall-Heroult electrolysis. Thus,Example I below shows that sufficiently low LOI values can be achievedfor this purpose.

The flash calciner may be built on the principles described in "AluminaCalcination in the Fluid-Flash Calciner" by William M. Fish, LightMetals 1974, Volume 3, The Metallurgical Society of the AmericanInstitute of Mining, Metallurgical and Petroleum Engineers, Inc., NewYork, N.Y., pages 673-682, and in "Experience with Operation of theAlcoa Fluid Flash Calciner" by Edward W. Lussky, Light Metals 1980, TheMetallurgical Society of AIME, Warrendale, Pa., pages 69-79. Alternativeequipment are (1) the F. L. Smidth calciner as described in a paperpresented at the AIME annual meeting in Dallas in February, 1982, by B.E. Raahauge et al and (2) the Lurgi/VAW calciner as described in theProceedings of the Second International Symposium of ICSOBA, Volume 3,pages 201-214 (1971).

The flash calciner schematically illustrated in FIG. 1C receives, e.g,boehmite particles through line 56 and brings them to temperatures inthe range 950° to 1220° C. by the action of the fuel through line 58 andthe hot gas (line 60) which supports the combustion of the fuel. Aluminaproduct is collected through line 62. Hot exhaust gases leave throughline 64 and are cleaned of entrained alumina in separator 66, withsolids being directed through line 68 to line 62 and hot exhausttraveling through line 40 to heat the decomposer.

B. Batch Process

The process of FIGS. 1A to 1C operates continuously. The portion in FIG.1B may be operated in a batch mode as illustrated in FIG. 2. FIG. 1numerals have been retained where the equipment is the same. Thismodification is achieved by substitution of a batch decomposer 70 andsuitable storage hoppers 72 and 74 to accommodate the still continuousfeeds through line 24 from the Bayer process and through line 56 to theflash calciner.

Batch decomposer 70 includes a lid 76, which may be moved between apressure-sealing position (shown) and an open position (not shown) byreleasing clamp 78 and rotating counterclockwise, say 95°, about hinge80. On the lower end of the decomposer is a floor 82. Lid 76 and floor82 form, together with side walls 84, a chamber 86. With floor 82 in theclosed position, as shown, pressure-sealing of chamber 86 is complete.Floor 82 can be rotated counterclockwise about hinge 85, upon release ofclamp 86, to open chamber 86 for emptying a batch of product.

Chamber 86 is heated by heat exchanger 88, which is located withinchamber 86 and provided with a flow of hot gas through lines 40 and 42.Electric heating is another option.

Back pressure regulator or valve 90, firstly, acts to prevent steam inline 50 from flowing back into decomposer 70 when the pressure in thedecomposer is still too low and, secondly, opens line 50 to steam onlyafter the desired pressure, e.g. 110 psia, has been achieved in thedecomposer.

In operation of the batch process, lid 76 is opened, and Al(OH)₃ fromhopper 72 is loaded into chamber 86 through line 25. The resulting bedself-fluidizes from the action of heat exchanger 88 in driving freemoisture and chemically combined water from the Al(OH)₃ particles.

As more and more water is driven off as steam, the pressure withinchamber 86 rises. Steam moves through line 44 to cyclone 46 as explainedabove for continuous operation. When the pressure on valve 90 builds upto a sufficient value, valve 90 opens and steam is supplied through line50 to the Bayer process.

When sufficient water has been removed, floor 82 is opened and e.g.boehmite product released from chamber 86 in direction 73 into hopper74.

Before valve 90 opens, the Bayer process can be supplied from anyauxiliary steam source supplying steam of desired pressure. Theauxiliary source can e.g. include a second decomposer 70 run inalternation with that illustrated in FIG. 2.

C. Products

The steam producing process of the invention as applied to Al(OH)₃ givesnew products.

Operating conditions of the pressure decomposer are: temperature:250°-650° C.; pressure (steam): 20-250 psig; and residence time: 10-120minutes. The hydrate decomposes under these conditions releasing wateras steam under pressure and producing a partially calcined alumina. Ourinvestigations have shown that the dehydration of alumina hydrate understeam pressure progresses by initial conversion of the trihydrate(gibbsite) to the oxide-hydroxide boehmite. The boehmite formed thendecomposes to gamma and/or X-ray indifferent, or amorphous, aluminapartially or fully depending on the temperature and residence time ofthe material in the decomposer.

Thus, the material coming from the decomposer is boehmite and gammaand/or X-ray indifferent alumina pseudomorphous with aluminum hydroxide.The boehmite content is usually relatively high, in the 10 to 50% range.Each particle is composed of a plurality of crystals. Loss on ignition(LOI) (300°-1200° C.) is in the range 1 to 12%, the lower water contentmaterial being obtained using the high portion of the e.g. 250° to 650°C. temperature range in the decomposer. Surface area will be in therange 10-100 m² /g (square meters per gram). Surface area data herein isBET, N₂ adsorption.

In the case where a high temperature, atmospheric pressure, i.e. at most10 psig (resulting from blowers to move the gases), calcination followsthe decomposer, the resulting alumina attains an LOI (300°-1200° C.) ofless than 1%, a surface area in the range of 10-100 m² /g, and amodified Forsytbe-Hertwig attrition index of 1 to 20.

Attrition index data herein is determined according to the method ofForsythe and Hertwig, "Attrition Characteristics of Fluid CrackingCatalysts", Ind. and Engr. Chem. 41, 1200-1206, modified in that samplesare attrited for only 15 minutes, this time having been found to bebetter for showing differences in aluminas.

Attrition Index I=100(X-Y)/X where

X=percent plus 325 mesh before attrition,

Y=percent plus 325 mesh after attrition.

The lower the attrition index, the higher is the resistance toattrition.

In general, the alumina product of the invention is much stronger, e.g.has a lower attrition index, than alumina made by calcining Al(OH)₃ atatmospheric pressure.

There are benefits in combining an initial pressure decomposition with aterminal atmospheric-pressure calcination. For instance, the terminalatmospheric-pressure calcination can be run at 850° C., or less, tobring LOI (300°-1200° C.) to 1% or below. This is to be compared to theover 950° C. required previously.

An additional benefit is the ability to arrive at an alumina product of1% LOI, or less, and of surface area in the range 10-100 m² /g, withoutproducing any alpha-alumina, a crystalline form of poor solubility inthe molten salt bath of a Hall-Heroult cell. In general, theatmospheric-pressure calcination converts the boehmite of theintermediate product to gamma alumina. Thus, 50% boehmite content in theproduct of the pressure decomposer will mean about 50% gamma aluminacontent in the product obtained by submitting the product of thepressure decomposer to an atmospheric-pressure calcination.

In both cases, decomposer only or decomposer plus calciner, the productis characterized by at least a reduced amount, and even an absence, ofthe parallel fissures so characteristic of the alumina that results fromaluminum hydroxide calcined at the zero, to perhaps at most the 7, or10, psig pressures previously used in dewatering the feed forHall-Heroult cells.

FIG. 3, compared with FIG. 4, illustrates this important characteristicof products according to the invention, namely the reduced amount, oreven absence, parallel fissuring.

The prior art product (Reference No. AP T182B) of FIG. 4 was prepared bycalcining Al(OH)₃ in a flash calciner as described in the above-citedarticles of Fish and Lussky. It measures 1 to 5% boehmite, restamorphous. As is evident from FIG. 4, the prior art product ischaracterized by parallel fissuring. This prior art alumina product hadan LOI (300°-1200 C.) of 0.94%, a surface area of 84 m² /g, and anattrition index of 15.

The product (Reference No. AP 4052-H2) of FIG. 3, which is a productaccording to the invention, was prepared by heating Al(OH)₃ at 500° C.,120 psig pressure, for one hour under self-fluidizing conditions andthen at 850° C., atmospheric pressure (0 psig), for one hour (the 850°C. treatment corresponding to a flash calcining operation). The productresulting from this treatment was about 50% gamma alumina, restamorphous, and had an LOI of 0.5%, a surface area of 51 m² /g and anattrition index of 6. Clear from a comparison of FIG. 3 with FIG. 4 is,in this example, a complete absence of parallel fissuring in the productof the invention.

It is thought that a beneficial result of the lack of parallel fissuringis an ability of the produ:t of the invention to be handled andtransported with a lesser production of fines as compared with materialhaving the parallel fissuring. In any event the product of the inventionis stronger, as evidenced by characteristically lower values of themodified Forsythe-Hertwig attrition index. Thus, for a given Al(OH)₃feed, it is possible to achieve consistently lower attrition indices forthe alumina feed for Hall-Heroult cells. For example, for a givenAl(OH)₃ feed, the attrition index will be at least 2 units lower for theproduct of the present invention than it would be for a product of thesame LOI achieved in an atmospheric pressure calcination. Furthermore,attrition indices lower than those of previous commercial aluminaproducts are obtainable in the present invention. Thus, it is known thatdifferent Al(OH)₃ feeds give different attrition indices in atmosphericpressure calcination. Lower attrition indices are said to result fromwell crystallized Al(OH)₃ while higher indices come from weaklycrystallized Al(OH)₃. Using well crystallized Al(OH)₃ in atmosphericpressure calciners, the lowest attrition indices previously obtainedwere 4 or 5. In the present invention, well crystallized Al(OH)₃ yieldsattrition indices of 2 or less.

Further illustrative of the invention are the following examples:

EXAMPLE I

A product (Reference No. AP 4203-6) was decomposed according to thepresent invention by transferring heat through the walls of a containerand into a bed of Al(OH)₃ in the container. The temperature in the bedwas 600° C. Heating was for a period of one hour. Pressure was 120 psig.The bed self-fluidized under the action of the gaseous water, steam,coming off the particles. There was no particle breakage during thisprocess, i.e. no increase in the weight of the -325 mesh size fraction.The product obtained by this procedure had an LOI (300°-1200° C.) of1.5%, a surface area of 94 m² /g and an attrition index of 4. X-raydiffraction analysis gives the following results: about 2% boehmite(X-ray diffraction pattern matching those of cards 5-0190 and 21-1307 ofthe Joint Committee on Powder Diffraction Standards, Swarthmore, Pa.),rest gamma and amorphous.

EXAMPLE II

A product (Reference No. AP 4064) was prepared according to the presentinvention by transferring heat through container walls and into a bed ofAl(OH)₃ in the decomposer container. Bed conditions were 500° C., 120psig pressure, one hour residence time. The material in the bedself-fluidized under the action of the gaseous water being evolvedduring decomposition. A product containing 28% boehmite resulted.Subsequently, the product of this high pressure treatment was heated at850° C., atmospheric pressure (0 psig), for one hour (this 850° C.treatment corresponding to a flash calcining operation). The finalproduct had an LOI (300°-1200° C.) of 0.5%, a surface area of 60 m² /gand an attrition index of 2. X-ray diffraction analysis gave thefollowing results: 0% boehmite, rest gamma and amorphous.

EXAMPLE III

Products of the invention were prepared as in Example II, except for thefollowing differences. Decomposer bed temperature was 400° C. Analysisof the product from the decomposer: surface area 40 m² /g, LOI 13.4%,attrition index 5, %-boehmite 44%. Analysis of the product from the 850°C., atmospheric-pressure calcining: LOI 0.5%, %-boehmite 0%, surfacearea 41 m² /g.

EXAMPLE IV

Products of the invention were prepared as in Example II, except for thefollowing differences. Decomposer bed temperature was 400° C., pressure200 psig, time at pressure 3/4 hour. Analysis of the product from thedecomposer: surface area 19 m² /g, LOI 16%, attrition index 9,%-boehmite 44%. Aralysis of the product from the 850° C.,atmospheric-pressure calcining: LOI 0.4%, %-boehmite 0%, surface area 30m² /g, attrition index 9.

EXAMPLE V

Products of the invention were prepared as in Example II, except for thefollowing differences. Decomposer bed temperature was 400° C., pressure60 psig, time at pressure 2 hours. Analysis of the product from thedecomposer: surface area 63 m² /g, LOI 11.3%, %-boehmite 30%. Theatmospheric-pressure calcining was at 750° C., again for 1 hour.Analysis of the product from this calcining was: LOI 0.9%, surface area65 m² /g and attrition index 6.

What is claimed is:
 1. A composition of matter comprising particles ofboehmite and gamma and X-ray indifferent alumina, the particles beingpseudomorphous with alumninum hydroxide, having an absence ofalpha-alumina, and having a reduced amount of parallel fissuring ascompared to any alumina from atmospheric pressure calcination ofaluminum hydroxide, each particle containing a plurality of crystals,the LOI (300°-1200° C.) of the particles being from 1 to 12%, theirsurface area being 10-100 m² /g.
 2. A composition of matter as claimedin claim 1, wherein there is an absence of parallel fissuring. 3.Alumina having a surface area in the range 10-100 m² /g, an attritionindex in the range 1-20, a reduced amount of parallel fissuring ascompared to any alumina from atmospheric pressure calcination ofaluminum hydroxide and an absence of alpha-alumina.
 4. Alumina asclaimed in claim 3, wherein surface area is in the range 10-70 m² /g. 5.Alumina as claimed in claim 3, wherein there is an absence of parallelfissuring.
 6. Alumina as claimed in claim 3, wherein the attrition indexis less than or equal to
 2. 7. Alumina as claimed in claim 3, whereinLOI (300°-1200° C.) is less than 1%.